Self-leak indicating package

ABSTRACT

A composite evacuated package for meat products and comprising a cup-like container shell of transparent semi-rigid plastic material with its opening sealed by thin flexible film. The film is stretched into the shell to engage the product, and atmospheric pressure transmitted through the film holds the product firmly against the opposite surface of the container shell in any orientational position of the package. A semi-rigid cover is press-fitted into the container opening, and is adapted for ready removal and subsequent reclosure after a portion of the product has been removed. This cover includes a central portion spaced from the flexible film, thereby defining between the film and the cover a normally unoccupied space which, when the package is inverted, is directly below the product. When in this position, the pressure equalization due to a leak in the package will permit the product to be moved by gravity down into that originally unoccupied space, so that the product correspondingly drops away from the opposite (now upper) surface of the container. Since the container is transparent, this displacement of the food product away from the exposed upper surface can readily be observed visually to identify a leaky package.

United States Patent Mahaffy et a1.

Assignee:

Filed:

Hamilton, Englewood, both of NJ.

Mahaffy & Harder Engineering Company, Totowa, NJ

Mar. 13, 1974 Appl. No.: 450,764

Related U.S. Application Data [63] Continuation of Ser. No. 52,629, July6, 1970,

abandoned.

'[52] US. Cl 426/129; 220/85 B; 229/49 [51] Int. Cl B65b 25/06 [58]Field 01 Search 420/413, 126, 129, 122, 420/106; 73/493, 52; 229/43;206/4534; 220/85 B; 53/112 R, 112 A [56] References Cited UNITED STATESPATENTS 1,825,699 lO/1931 Landrum 73/52 X 1,833,752 11/1931Longchamp.... 220/42 B 2,621,129 12/1952 Rambbottom.. 426/127 2,754,9597/1956 Mc Carly 426/129 3,047,993 8/1962 Robbins 73/493 X 3,087,8234/1963 Mein 426/122 3,116,153 12/1963 Seiferth 426/106 3,214,221 10/1965Finnegan 426/413 3,216,832 11/1965 King 53/112 X 3,226,236 12/1965Weller 206/4534 X 3,298,158 1/1967 Schmidt 53/112 A 3,396,899 8/1968Strouse 229/43 3,467,244 9/1969 Mahaffy... 206/4534 3,498,018 3/1970Seifeith 206/484 X Primary Examiner-Robert Halper Attorney, Agent, or FirmParmelee, Johnson & Bollinger ABSTRACT A composite evacuated packagefor meat products and comprising a cup-like container shell oftransparent semi-rigid plastic material with its opening sealed by thinflexible film. The film is stretched into the shell to engage theproduct, and atmospheric pressure transmitted through the film holds theproduct firmly against the opposite surface of the container shell inany orientational position of the package. A semi-rigid cover ispress-fitted into the container opening, and is adapted for readyremoval and subsequent reclosure after a portion of the product has beenremoved. This cover includes a central portion spaced from the flexiblefilm, thereby defining between the film and the cover a normallyunoccupied space which, when the package is inverted, is directly belowthe product. When in this position, the pressure equalization due to aleak in the package will permit the product to be moved by gravity downinto that originally unoccupied space, so that the productcorrespondingly drops away from the opposite (now upper) surface of thecontainer. Since the container is transparent, this displacement of thefood product away from the exposed upper surface can readily be observedvisually to identify a leaky package.

7 Claims, 9 Drawing Figures llLlllI/llllll/lll/Mlllll.I11 III SELF-LEAKINDICATING PACKAGE I This is continuation, of application Ser. No.052,629 filed July 6, 1970 now abandoned.

This invention relates to an improved package for sliced luncheon meats,frankfurters. sliced bacon and other perishable food products. Moreparticularly, this invention relates to a self leak-indicating packagewith three elements: a semi-rigid cup, a thin flexible film for hermeticsealing, and a semi-rigid cover.

It is known to package meat products such as those mentioned above in asemi-rigid plastic package utilizing vacuum or inert gases as disclosedin copending applications Ser. No. 484,249 now abandoned, filed Sept. 1,1965 by W. E. Young and Reid A. Mahaffy, and Ser. No. 484,284 nowabandoned, filed Sept. 1, 1965 by Reid A. Mahaffy, et al., and asdisclosed in US. Pat. No. 3,467,244, issued Sept. 16, 1969. Therein areshown unique packages consisting of thermoformed semi-rigid plasticshells, into which the food product is inserted, sealed withthermoformed flexible plastic film conforming generally to the shape ofthe products packaged therein.

Although such packages have found acceptance commercially, theirstructures have not been entirely satisfactory for some applicationsbecause: (a) the flexible film is sometimes damaged or otherwisedestroyed during opening, thereby limiting the ability to reclose thepackage; and (b) in the case of packages with an added planar stiffcover, the closure combination of the flexible film and planar cover maynot stay in place when reclosed.

It is desirable to provide vacuum packages having all of theadvantageous features of the above-mentioned prior packages but alsohaving the capability of being more readily reclosed after part of theproduct has been used. With the continuing increase in size or amount offood products held in a single package, the need for a good reclosurearrangement has become particularly important.

In addition, it is desirable to provide such packages with means toindicate visually if there has been a leak of air into the packageinterior.

Accordingly, it is an object of the present invention to provideimproved semi-rigid packages. A more specific object is to provide suchpackages having improved reclosure means. Still another object is toprovide a self-leak-indicating package having the aforementionedadvantages. Yet another object is to provide such a package withincreased puncture resistance. A more general object is to provide animproved package accomplishing the foregoing at low cost.

A preferred vacuum package in accordance with this invention comprisesthree elements: (1) a transparent semi'rigid cup-like container shell ofoxygen-barrier plastic material for holding the food product, (2) aflexible plastic film of oxygen-barrier material sealed to the marginalflanges of the container and stretched downwardly into contact with thefood product, and (3) a semi-rigid plastic closure member or cover ofnon-oxygen-barrier material, press-fitted into the container opening andproviding protection from abuse, puncture, etc., for the flexible film.In use, the customer first peeels off the semi-rigid cover, then stripsaway the flexible film in the usual fashion, and thereafter removes theportion of the product desired. Subsequently, the semi-rigid cover canbe refitted into place in the container opening, to protect thoseportions of the product still remaining in he container.

The package is evacuated to such an extent that the product is heldpressed at least lightly against the central face of the transparentshell (i.e. the bottom bottom of the cup), in any orientational positionwith respect to gravity. The semi-rigid cover is spaced a short distanceaway from the flexible film (where the latter contacts the product),thereby defining between the cover and the film a normally unoccupiedregion which is atmospheric pressure. When the package container isdisplayed inverted, (i.e. so that the bottom face of the container shellis the display face of the package), this unoccupied region will bedirectly beneath the product.

In that inverted display position, equalization of pressure across theflexible film resulting from a leak in the package will permit theproduct to be urged by gravity down against the flexible film (no longerheld tautly against the product) and into the previously unoccupiedregion immediately above the semi-rigid cover. If that occurs, one canreadily detect the event visually by observing through the transparentdisplay face of the container shell that the product no longer ispressed against the inner surface of the display face. Thus the packageincludes self-indicating means automatically operative to show that thepackage integrity has been breached with a leak.

Other objects, aspects and advantages of the present invention will inpart be pointed out in, and in part apparent from, the followingdetailed description considered together with the accompanying drawings,i which:

FIG. 1 is a perspective viewof a semi-rigid frankfurter package inaccordance with the present invention;

FIG. 2 is a vertical cross-section of the package of FIG. 1;

FIG. 3 is a view like FIG. 2, but showing the relative positions of thepackage elements after the package has developed a leak;

FIG. 4 is a vertical cross-section of a semi-rigid package showing amodified cover structure;

FIG. 5 is a vertical cross-section showing still another different coverstructure;

FIG. 6 is a detail section showing a modified form of the package ofFIG. 5;

FIG. 7 is a vertical cross-section showing a package like that of FIG.5, but with the semi-rigid cover pressed against the film and product;

FIG. 8 is a vertical cross-section of a semi-rigid package containingsliced luncheon meat; and

FIG. 9 is a detail cross-section showing a detent holding arrangementfor a package such as in FIG. 8.

REferring now to FIGS. 1 and 2, there is shown a three-element evacuatedpackage 10 which includes as one element a thermoformed transparentplastic semirigid container shell in the form of an inverted cup-likemember 12. This shell is substantially filled with a food product 14,illustratively frankfurters. The container is made of laminatedoxygembarrier plastic material, such as PVC, saran and polyethylene, andof sufficient thickness to be semi-rigid, i.e. form-retaining. Thecontainer preferably is formed with a shape matching that of thecontained product.

Pressed up against the bottom surfaces of the product 14 is a flexible,oxygen-barrier plastic film 16. This film is heat-sealed to the marginalflanges 18 of the cup, and is stretched up into the container openingagainst the lower surfaces of the product. With the package evacuated,and thus at reduced internal pressure, the product is pressed up againstthe top face of the container shell by atmospheric pressure transmittedthrough the thin plastic film. The film also engages tightly the innerside walls of the container, and holds the product firmly in position.The flexible film may be made of a combination of thin flexiblepolyester with saran and polyethylene, and preferably includes a heatsealable and peelable overcoating applied to its sealing surface.

The package may after evacuation be partially filled with an inert gas,but at a pressure sufficiently low that atmospheric pressure, actingthrough the film 16, will hold the product againt the inner surface ofthe semirigid container 12, regardless of the positional orientation ofthe package with respect to gravity.

A pre-formed plastic semi-rigid cover or closure member 22 ispress-fitted into the opening of the container 12. This covermay, ifdesired, be secured to the flexible film 16 by heat sealing, byadhesive, or by any other convenient method, so that it will be heldfirmly in place through the merchandising cycle of the package. Thecover is dimensioned to provide a close, friction-fit within the sidewalls of the semi-rigid container. shell. Since the package ishermetically sealed by film 16, this cover 22 need not be made ofmaterial having a low rate of oxygen permeability, but mayadvantageously be formed of relatively inexpensive plastic material suchas polystyrene. The rigidity of the cover effectively prevents damage,such as puncture, to the somewhat fragile film l6, and thus performs animportant role in maintaining the package integrity, as well asaffording a superior reclosure capability as will be described.

As shown particularly in FIG. 2, the semi-rigid cover 22 is soproportioned and dimensioned that when it is fitted in place in thecontainerv 12, its recessed central portion 24 is spaced a moderatedistance away from the flexible film 16 in contact with the food product14. With this arrangement, a corresponding unoccupied region 26 isdefined between the cover and the film. This region ordinarily will beat atmospheric pressure. In the horizontal inverted display position ofthe package (as shown), wherein the central face 28 of the containershell (i.e. what might be called the bottom of the cup-like shell)serves as the product display face,

this unoccupied region 26 is directly beneath the product.

The packaged product 14 normally is held against the display face 28 byatmospheric pressure acting through the flexible film 16. However, ifthe package leaks, so that the differential pressure across the flexiblefilm becomes substantially reduced, the product will drop down into theregion 26 due to the force of gravity. Under most circumstances, theproduct will move down sufficiently to come to rest against the centralportion 24 of the semi-rigid cover 22, as shown in FIG. 3, In any event,the product will move down to a new position where it is out of contactwith the inner surface of the display face 28, and this abnormalcondition will readily be apparent to an observer, e.g. the manager ofthe store, or a customer, because of the transparency of the displayface. Thus the package provides in this manner an automatic tell-taleindication that a leak has occurred.

If the package is displayed in a vertical position, e.g., hung from apeg passing through a hole 30 in an extended flange 32 of the shell 12,the same advantageous leak-indication will be obtained. This is becausea component of the gravity force will tend to move the product back awayfrom the display face 28. That is, when the pressure differential acrossthe film 16 is equalized by a leak, the product will fall away from thedisplay face and into the region 26.

FIG. 4 illustrates a modified semi-rigid plastic cover 22A which may beused to enable a greater volume of the semi-rigid container shell to befilled with product. The central portion 24A of the semi-rigid cover isnot recessed, as in FIG. 2. Instead, this central portion is alignedwith the flanges of the container, i.e. in the plane of the containeropening. However, the cover includes side wall projections 34 whichextend into the interior of the container adjacent all four sides, to engage the container side walls in a friction fit as in the FIG. 2arrangement. For some applications projections may be provided onlyalong two opposite sides. The central portion 24A is made sufficientlylarge to permit the packaged products 14 to move down into the region26A when the package develops a leak.

When the food product 14 consists of chunks or individual sausages, asshown in the illustrative embodiments described hereinabove, it often isdesirable to use an inert gas to fill the voids between the products andbetween the products and the inner surfaces of the package. Still it isdesirable, even when using inert gas, to hold as many products aspossible, over as large an area as possible, in contact with the displayface of the package. Thus the display face 28 (28A) is shaped to conformclosely to the outlines of the products, and the flexible film 16 isthennoformed to fit snugly against the opposite surfaces of theproducts. FIG. 5 shows that the semi-rigid cover 228 may also be shapedwith a conformation matching the outline of these opposite surfaces.

Referring now to FIG. 6, when using a productconformed semi-rigid cover(like FIG. 5), it may be advantageous for packages with rectangular planoutlines, to relieve the corners of the cover 22C, i.e. so as to avoidforming elements which project inwardly any substantial distance towardsthe product in the corner regions. Although the cover does include arecessed central portion 24C arranged to fit tightly against the sidewalls of the container opening, this portion is provided with inwardlyprojecting contour-matching elements 24D, only in the regions betweenpairs of frankfurters, not between a frankfurter and an adjacent wall ofthe container. This configuration minimizes any chance that the inwardlystretched corners of the flexible film might be punctured by projectionson the semirigid cover. This can be of particular importance becauseit'is difficult to stretch the film into precise conformation with theedge surfaces of the product in the corners of the shell.

Only a small amount of inert gas is inserted into the package, so thatthe pressure of atmosphere exerted through film 16 is sufficient toforce the product against the display face 28 and hold the productsecurely in place when the package is oriented with the display face asthetop of the package, as shownv For some product applications, it maybe desirable to hold the product securely in position even though a leakoccurs. This may be accomplished, as shown in FIG. 7, by

shaping the semi-rigid cover in such a profile as to press theproductagainst the display surface by mechanical pressure alone. Whenusing this construction in a square or rectangular packageconfiguration, the cover may be relieved in the comer regions (asillustrated in FIG. 6), for the same purpose of minimizing thepossibility of puncturing the flexible film where it may not have beenstretched entirely into conformity with the shell and product.

FIG. 8 shows a package 40 having a round outline in a plane view andadapted to hold sliced luncheon meat. This package comprises asemi-rigid container cup 42 of oxygen-barrier material, a flexible film44 of oxygenbarrier material stretched inwardly into tight contact withthe product, and a semi-rigid cover 46 of non-oxygen-barrier material.The cover has a recessed central portion 48 which is spaced a shortdistance away from film 44, to define a normally unoccupied region whichserves the same leak-detecting function as region 26 previously referredto.

As shown in FIG. 9, the semi-rigid cup 42 and the semi-rigid cover 46may be provided with interlocking detents 50 and 52 to hold the coversecurely in position, after the package has been reclosed followingremoval of part of the product. For most circumstances, two such detentsshould be sufficient, on opposite sides of the package, but additionaldetents may be incorporated where appropriate. The flexible film 44follows the profile of the cup detent allowing the matching detent ofthe cover to engage the cup detent with the flex ible film in place. Theformation of the flexible film is accomplished by methods and apparatusdisclosed in the above-identified co-pending applications, and inco-pending application Ser. No. 849,248, filed on July 30, 1969 by ReidA. Mahaffy, et al.

Various modifications in the configuration and arrangement of thethree-element plastic package forming the subject matter of theinvention will be apparent to those skilled in the art and such areconsidered to be within the scope and spirit of the invention as recitedin the description and set forth in the appended claims.

We claim:

1. A package for perishable food products comprising a semi-rigidplastic cup of oxygen-barrier material having marginal flanges andcontaining a food product filling only a portion of the cup volume belowsaid flanges;

a thin flexible film of oxygen-barrier material peelably sealed to saidflanges and stretched down into said cup along the side surfacesthereof, the interior portions of said flexible film serving to engageand press against the food products tightly across the full uppersurface thereof, the interior of the cup being evacuated so thatatmospheric pressure against the flexible film forces the food productsagainst the bottom surface of the cup; and

a semi-rigid plastic cover of non-oxygenbarrier material comprisingouter flanges and a recessed central section telescoped into the cup;

the outer side walls of said central section being tightly engaged in afriction-fit with the inner surface of said flexible film where it isstretched into the cup down towards the product, said central sectionbeing spaced a moderate distance from said flexible film;

the lateral dimension of said recessed central section beingsufficiently large to provide a tight fit within said cup after l) thecover has been removed, (2) the flexible film removed, and then (3) thecover has been replaced following removal of a portion of the product; Isaid recessed central section and said semi-rigid cup being constructedand arranged to provide interengageable means cooperatively operableafter the cover has been reinserted with the flexible film removed fromthe region adjacent the side surfaces of said cup to provide a grippingfit effecting retention of the cover after said removal of said flexiblefilm; said plastic cover extending over the entire opening of saidplastic cup, and cooperating with said semirigid plastic cup inproviding physical protection for the contained product while saidflexible film and said plastic cup cooperate to sealingly isolate saidproduct from outside atmosphere. 2. A package as in claim 1, whereinsaid interengageable means comprises an outwardly extending lip on theinterior surface of said recessed central portion and a cooperatinginwardly extending ridge on the inner wall surface of said semi-rigidcup, said lip being located interiorly of said ridge when said cover isin place in said cup so as to provide engagement there between to retainsaid cover positively in position.

3. The method of detecting the leakage of an evacuated packagecontaining a spoilable food product or the like, comprising:

inserting the product into a semi-rigid cup-like container havingmarginal flanges around the opening thereof and with the product lateraldimensions being so selected that the product will fall down away fromthe cup-bottom surface when the container is held in its invertedposition; said cupbottom surface being of non-opaque material;

positioning said product fully in engagement with said cup-bottomsurfaces throughout the entire area of said surfaces, at leastsubstantially free from any open-space regions between said product andsaid cup-bottom surfaces, thereby to ensure that the outside appearanceof said cup-bottom surface distinctively indicates that said product isfully in engagement therewith;

sealing a flexible film to said marginal flanges and forcing said filmby atmospheric pressure into said cup and against said product with thepackage evacuated;

placing at said cup opening a semi-rigid cover having a central portionspaced a Significant distance from said flexible film where it is incontact with said product;

orienting the package with the food product forced by gravity downtowards said flexible film and with said cup-bottom surface presentedfor inspection by an observer", and

detecting the occurrence of a leak by observing the difference inappearance between (1) the package cup-bottom surface as presented tothe observer with the product fully in contact with said surface, and(2) the package cup-bottom surface as presented to the observer with theproduct spaced down away from said surface said significant distance asa result of gravity forcing said product down against said flexible filmtowards said semirigid cover.

4. The method of claim 3, wherein said product has an undulating surfacefacing towards said cup-bottom surfaces; and

forming said cup-bottom surfaces with undulations matching said productundulations, whereby to ensure that said product engages said cupbottomsurfaces throughout the entire area thereof.

5. The method of claim 3, wherein said semi-rigid cover is formed with arecessed section telescoped into the opening of said container andhaving side walls which are pressed outwardly against, and infrictiontight engagement with, the inner side wall surfaces of saidcontainer.

6. A package for perishable food products comprising a semi-rigidplastic cup of oxygen-barrier material having marginal flanges aroundthe opening thereof and containing a product the upper surfaces of whichare at least predominately below said flanges;

a thin flexible film of oxygen-barrier material sealed to said flangesand stretched down into said cup along the side surfaces thereof, theinterior portions of said flexible film serving to engage and pressagainst the upper surface of said product, the interior of the cup beingevacuated so that atmospheric pressure against the flexible film forcesthe product against the bottom surface of the cup; and

a semi-rigid plastic cover comprising outer flanges matched with theflanges of said cup and having a said outer side walls of said centralsection being engaged in a friction-fit with the inner surface of saidflexible film where it is stretched into the cup down towards theproduct, said central section being dimensioned so as to be locatedabove the upper surfaces of said product and its engaging film for therange of product depths to be encountered;

the lateral dimensions of said recessed central section beingsufficiently large to provide a close fit within said cup after l) thecover has been removed, (2) the flexible film has been removed, and then(3) the cover has been replaced following removal of a portion of theproduct;

said recessed central section and said semi-rigid cup being constructedand arranged to provide interengageable means cooperatively operableafter the cover has been reinserted to effect retention of the coverafter said removal of said flexible film;

said plastic cover extending over the entire opening of said plastic cupto cooperate with said semi-rigid plastic cup in providing physicalprotection for the contained product while said flexible film and saidplastic cup cooperate to sealingly isolate said product from outsideatmosphere.

7. A package as claimed in claim 6, wherein said interengageable meanscomprises a detent arrangement with mating components on said cover andsaid cup respectively.

1. A PACKAGE FOR PERISHABLE FOOD PRODUCTS COMPRISING A SEMI-RIGIDPLASTIC CUP OF OXYGEN-BARRIER MATERIAL HAVING MARGINAL FLANGES ANDCONTAINING A FOOD PRODUCT FILLING ONLY A PORTION OF THE CUP VOLUME BELOWSAID FLANGES: A THIN FLEXIBLE FILM OF OXYGEN-BARRIER MATERIAL PEELABLYSEALED TO SAID FLANGES AND STRETCHED DOWN INTO SAID CUP ALONG THE SIDESURFACES THEREOF, THE INTERIOR PORTIONS OF SAID FLEXIBLE FILM SERVING TOENGAGE AND PRESS AGAINST THE FOOD PRODUCTS TIGHTLY ACROSS THE FULL UPPERSURFACE THEREOF, THE INTERIOR OF THE CUP BEING EVACUATED SO THATATMOSPHERIC PRESSURE AGAINST THE FLEXIBLE FILM FORCES THE FOOD PRODUCTSAGAINST THE BOTTOM SURFACE OF THE CUP, AN A SEMI-RIGID PLASTIC COVER OFNON-OXYGEN-BARRIER MATERIAL COMPRISING OUTER FLANGES AND A RESESSEDCENTRAL SECTION TELESCOPED INTO THE CUP, THE OUTER SIDE WALLS OF SAIDCENTRAL SECTION BEING TIGHTLY ENGAGED IN A FRICTION-FIT WITH THE INNERSURFACE OF SAID FLEXIBLE FILM WHERE IT IS STRETCHED INTO THE CUP DOWNTOWARDS THE PRODUCT, SAID CENTRAL SECTION BEING SPACED A MODERATEDISTANCE FROM SAID FLEXIBLE FILM, THE LATERAL DIMENSION OF SAID RECESSEDCENTRAL SECTION BEING SUFFICIENTLY LARGE TO PROVIDE A TIGHT FIT WITHINSAID CUP AFTER (1) THE COVER HAS BEEN REMOVED, (2) THE FLEXIBLE FILMREMOVED, AND THEN (3) THE COVER HAS BEEN REPLACED FOLLOWING REMOVAL OF APORTION OF THE PRODUCT. SAID RECESSED CENTRAL SECTION AND SAIDSEMI-RIGID CUP BEING CONSTRUCTED AND ARRANGED TO PROVIDEINTER-ENGAGEABLE MEANS COOPERATIVELY OPERABLE AFTER THE COVER HAS BEENREINSERTED WITH THE FLEXIBLE FILM REMOVED FROM THE REGION ADJACENT THESIDE SURFACES OF SAID CUP TO PROVIDE A GRIPPING FIT EFFECTING RETENTIONOF THE COVER AFTER SAID REMOVAL OF SAID FLEXIBLE FILMS. SAID PLASTICCOVER EXTENDING OVER THE ENTIRE OPENING OF SAID PLASTIC CUP, ANDCOOPERATING WITH SAID SEMI-RIGID PLASTIC CUP IN PROVIDING PHYSICALPROTECTION FOR THE CONTAINED PRODUCT WHILE SAID FLEXIBLE FILM AND SAIDPLASTIC CUP COOPERATE TO SEALINGLY ISOLATE SAID PRODUCT FROM OUTSIDE ATM2. A package as in claim 1, wherein said interengageable means comprisesan outwardly extending lip on the interior surface of said recessedcentral portion and a cooperating inwardly extending ridge on the innerwall surface of said semi-rigid cup, said lip being located interiorlyof said ridge when said cover is in place in said cup so as to provideengagement there between to retain said cover positively in position. 3.The method of detecting the leakage of an evacuated package containing aspoilable food product or the like, comprising: inserting the productinto a semi-rigid cup-like container having marginal flanges around theopening thereof and with the product lateral dimensions being soselected that the product will fall down away from the cup-bottomsurface when the container is held in its inverted position; saidcup-bottom surface being of non-opaque material; positioning saidproduct fully in engagement with said cup-bottom surfaces throughout theentire area of said surfaces, at least substantially free from anyopen-space regions between said product and said cup-bottom surfaces,thereby to ensure that the outside appearance of said cup-bottom surfacedistinctively indicates that said product is fully in engagementtherewith; sealing a flexible film to said marginal flanges and forcingsaid film by atmospheric pressure into said cup and against said productwith the package evacuated; placing at said cup opening a semi-rigidcover having a central portion spaced a significant distance from saidflexible film where it is in contact with said product; orienting thepackage with the food product forced by gravity down towards saidflexible film and with said cup-bottom surface presented for inspectionby an observer; and detecting the occurrence of a leak by observing thedifference in appearance between (1) the package cup-bottom surface aspresented to the observer with the product fully in contact with saidsurface, and (2) the package cup-bottom surface as presented to theobserver with the product spaced down away from said surface saidsignificant distance as a result of gravity forcing said product downagainst said flexible film towards said semi-rigid cover.
 4. The methodof claim 3, wherein said product has an undulating surface facingtowards said cup-bottom surfaces; and forming said cup-bottom surfaceswith undulations matching said product undulations, whereby to ensurethat said product engages said cup-bottom surfaces throughout the entirearea thereof.
 5. The method of claim 3, wherein said semi-rigid cover isformed with a recessed section telescoped into the opening of saidcontainer and having side walls which are pressed outwardly against, andin friction-tight engagement with, the inner side wall surfaces of saidcontainer.
 6. A package for perishable food products comprising asemi-rigid plastic cup of oxygen-barrier material having marginalflanges around the opening thereof and containing a product the uppersurfaces of which are at least predominately below said flanges; a thinflexible film of oxygen-barrier material sealed to said flanges andstretched down into said cup along the side surfaces thereof, theinterior portions of said flexible film serving to engage and pressagainst the upper surface of said product, the interior of the cup beingevacuated so that atmospheric pressure against the flexible film forcesthe product against the bottom surface of the cup; and a semi-rigiDplastic cover comprising outer flanges matched with the flanges of saidcup and having a recessed central section having outer side wallsextending down into the cup; said outer side walls of said centralsection being engaged in a friction-fit with the inner surface of saidflexible film where it is stretched into the cup down towards theproduct, said central section being dimensioned so as to be locatedabove the upper surfaces of said product and its engaging film for therange of product depths to be encountered; the lateral dimensions ofsaid recessed central section being sufficiently large to provide aclose fit within said cup after (1) the cover has been removed, (2) theflexible film has been removed, and then (3) the cover has been replacedfollowing removal of a portion of the product; said recessed centralsection and said semi-rigid cup being constructed and arranged toprovide inter-engageable means cooperatively operable after the coverhas been reinserted to effect retention of the cover after said removalof said flexible film; said plastic cover extending over the entireopening of said plastic cup to cooperate with said semi-rigid plasticcup in providing physical protection for the contained product whilesaid flexible film and said plastic cup cooperate to sealingly isolatesaid product from outside atmosphere.
 7. A package as claimed in claim6, wherein said interengageable means comprises a detent arrangementwith mating components on said cover and said cup respectively.